This invention relates to a power generator for supplying a high-frequency high-voltage, comprising an active element, a frequency-determining circuit connected in series to the AC main current path of the active element and a control circuit connected to a control electrode of the active element.
Such a power generator is known from Dutch Patent Specification No. 67258 (U.S. Pat. No. 2,554,087).
For operating high-frequency heating equipment for industrial applications such as, for example, plasma torches, it is deemed desirable to generate a high-frequency high-voltage having a large power.
From said Dutch Patent Specification No. 67258 a power generator is known for inductively heating a workpiece. This workpiece causes appreciable damping of the frequency-determining circuit, which implies that the resonance resistance of the frequency-determining circuit has a low value. In order to attain a reasonable efficiency of the power generator, the impedance of the frequency-determining circuit is stepped up. As a result, the AC output voltage of the active element is stepped down, whereas many high-frequency heating processes actually require a high AC output voltage.
In the power generator said Dutch Patent Specification No. 67258 the maximum attainable operating frequency is restricted by the presence of parasitic reactances. For example, in parallel with the induction coil in the frequency-determining circuit there is always a relatively large parasitic capacitance. This capacitance limits the maximum attainable operating frequency.
It is likewise desirable to protect the active element from overload failure at a given maximum supply voltage.